It is customary in the prior art that when constructing a seam to join together two carpet pieces along respective straight edges thereof, a tape is glued behind the carpet pieces along the seam. The tape is usually provided with beads extending therealong. In the installation, the glue is melted with a hot iron which is positioned over the top surface of the tape with the carpet pieces being positioned on the melted glue as the hot iron is moved. The carpet is pressed against the tape when the glue is hot so that the carpet will adhere to as it cools. However, during the cooling stage the tape has a tendency to arch upwards due to the opposed pulling forces by the carpet edges which have a tendency to lift. The end result is that often the carpet will peak along its formed seam resulting in a longitudinal bump within the carpet surface at the seam. To reduce this problem, weights can be placed immediately over the seam while the glue on the tape is cooling.
During installation, the carpet is stretched from the outer edges thereof to pull the carpet taut to remove bumps therein, and the carpet is engaged by the nail strips which are secured along the outer periphery of the area to be carpeted. This stretching force is applied to both carpet pieces resulting in a transverse force being applied to the tape from both sides of the tape by the carpet pieces secured thereto. The carpet thus has a tendency to want to separate at the seam, which is the weakest point. This is particularly so if the glue on the surface of the tape has not set completely into the carpet backing. The result can be a separation of the seam or the carpet seam can peak.
Another disadvantage in the assembly of the seaming tape to the backing of adjoining edge portions of carpet pieces is that because the carpets are positioned over an undercushion, usually made of polyurethane, rubber, felt, foam, or other similar material, it is difficult to apply good bonding pressure between the tape and the backing of the carpet pieces along the seam. Therefore, in order to add more resistance and support to the tape to enable the carpet installer to exert the needed downward pressure to set the carpet in the soft melted adhesive, it is customary to make the seam over a rigid floor surface area, or to position a strip of rigid board material under the seaming tape, see U.S. Pat. No. 3,660,191. These methods are very cumbersome and time consuming.
The problem of peaking is also common when carpeting a staircase wherein a seam ends up near a stair nose where the downward slant of the carpet will hinge out at the seam. Also, if a seam is disposed on an uneven or bumpy floor, peaking will occur when the undersurface of the carpet is not flat. Still further, peaking will occur where there is a joint between underlays of different thickness, such as in hallways or doorways leading to an adjoining carpeted area. The same problem occurs when the seam is close to the wall as the carpet strippers which are secured to the floor along the wall are often thinner than the underpad. In all these cases, peaking occurs at the seam because the backing tape is not rigid and offers no resistance to the upward force along the edge of the carpet pieces which have a tendency to curl upwards, and cause the backing tape to hinge and thereby forming a longitudinal fold therealong.
Particular reference is made to U.S. Pat. No. 2,552,114 which discloses a carpet joining device consisting of a saddle clip which is disposed spaced apart and transversely over a strip of paper and provided with sharp prongs or grippers on a top side which penetrate into the backing of carpet pieces to maintain them in position along a seam. These clips were particularly useful to retain the carpet pieces in immovable position when the carpet has a pattern therein to retain the alignment in the patterns on both sides of the seam of the carpet pieces. The grippers also hold the edges in abutting relationship during the stretching operation and thereafter as disclosed. During installation, a liquid glue is applied on the top surface of the backing paper.
These saddle clips are also often riveted into a floor surface to provide stability and to maintain the carpet stationary along the seam so that the stresses induced therein by stretching would not cause the seam to open, as the glue is usually still in liquid form when the carpet is being stretched. These saddle clips therefore provide for a quicker installation as it is not necessary to let the glue set completely. It is also pointed out that the grippers or prongs penetrate into the carpet pile and render it dangerous to a person walking on the carpet with bare feet. It is therefore recommended that when installing these saddle clips the grippers or prongs be bent back by striking them with a hard object, such as a hammer.
A major disadvantage of the tape as disclosed in the above-mentioned U.S. patent is that it cannot use meltable adhesive, as the prongs would prevent a hot iron from being placed in contact with the adhesive. The saddle clips must therefore be used in a method where liquid adhesive is used at the time of installation. Therefore, it is difficult and time consuming to install this type of seaming device. Still further, because of the tension that is applied to the surface of the carpet when connecting them to the peripheral grippers, these prongs can rip the backing material of the carpets along the seam area where the glue is still in liquid form, and the carpet seam can open and the saddle clip can buckle upwards and cause peaking. These saddle clips are not in common use due to these disadvantages, and particularly the fact that they are time consuming to install.